A Novel de Novo 20q13.11q13.12 Microdeletion in a Boy with Neurodevelopmental Disorders − Case Report

Abstract Copy-number variants (CNVs) are an important cause of human neurodevelopmental disorders. We present the first case of a 424 kb de novo 20q13.11q13.12 microdeletion in a patient with attention deficit disorder, tics and autistic behaviors, such as emotional and behavioral problems, and movement stereotypes. This region includes three genes expressed in the brain: SFRS6, PTPRT and L3MBTL. Our results suggest that loss of the chromosomal region 20q13.11q13.12 is causative for the clinical findings observed in the patient.


INTRODUCTION
Neurodevelopmental disorders are a group involving developmental impairments of the central nervous system. ese include intellectual disability (ID), autism spectrum disorders (ASDs), attention de cit hyperactivity disorder (ADHD), impaired motor function, learning, language or non-verbal communication and tics [1]. Epidemiological studies have identi ed various risk factors for neurodevelopmental disorders. Submicroscopic chromosomal copy-number variants (CNVs) are some of the contributing factors. Because of the large genetic heterogeneity of neurodevelopmental disorders, high-resolution whole-genome analyses, such  [2]. Moreover, the advent of aCGH technologies has paved the way to the discovery of novel genes. We have identi ed and characterized a novel microdeletion in the 20q13.11q13.12 region in a boy with emotional and behavioral problems, movement stereotypes, tics and attention de cit disorder; we further report on associated clinical and neurological ndings in the patient.

MATERIAL AND MOLECULAR INVESTIGATION
e patient was born to non-consanguineous parents at 40 Hbd weeks of gestation by caesarean section. Body parameters were within the normal range with birth weight of 3250 g, body length 58 cm and head circumference 34 cm. Early developmental milestones were normally attained. At school age (from age 6) he was noted to have stereotyped movements, nervous tics, social and emotional disturbances, and attention de cit disorder. Currently -at age 13 − he still manifests nervous tics in stressful situations. He has been diagnosed with dyslexia, dysgraphia, attention de cit disorder and continues to have learning di culties. His intelligence is assessed at average level. No signi cant dysmorphic characteristics have been observed aside from a slightly asymmetric and narrow chest, small ears, and synophrys. EEG analysis showed discrete changes on the right temporal area. e family history is positive for Asperger syndrome in his father's brother, depression in his mother and schizophrenia in his paternal grandmother.
Oligonucleotide array comparative genomic hybridization (aCGH) was performed using 8x60K from Oxford Gene Technology (CytoSure ISCA v2). Array CGH has genome-wide coverage with an average resolution of 120 kb. DNA digestion, labeling, and hybridization were performed following the manufacturer's instructions.

DISCUSSION
We performed a literature review and database search for individuals carrying a microdeletion involving the long arm of chromosome 20. To date, there are very few medical reports of 20q13 deletion, most of which involve regions more distal to our case [3][4][5]. We present, to our knowledge, the rst case of 20q13.11q13.12 microdeletion encompassing the PTRP gene in a patient with neurodevelopmental disorder. e deleted region observed in our patient includes three genes: PTPRT, SFRS6 and L3MBTL expressed in many tissues, mostly in the brain. Two of these genes (PTPRT and L3MBTL) are haploinsu cienct (sensitive to haploinsu ciency). e PTPRT gene is the candidate gene in the 20q13.11q13.12 region most likely associated with the pathology identi ed in our patient. Receptor protein tyrosine phosphatase (PTPRT) is a transmembrane protein that interacts with other cell adhesion molecules and regulates a variety of cellular processes including cell growth, di erentiation, mitotic cycle, and oncogenic transformation. e PTPRT protein is a regulator of synaptic formation and neuronal development [6]. Overexpression of PTPRT in hippocampal neurons correlates with synaptic formation and dendritic arborization. On the other hand, knockdown of PTPRT decreased neuronal transmissions and attenuated neuronal development [6]. PTPRT was identi ed as a potential candidate gene for autism spectrum disorders (ASDs). A genome-wide association study found suggestive linkage results between the chromosome region 20q11.21 and ASDs [7]. One of the autism candidate genes of interest in this region was reported to be PTPRT. Further, Christian et al. identi ed an inherited duplication including this gene in a patient with ASDs [8]. A large group of the genes identi ed as risk factors for ASD plays an important role in synaptic homeostasis [9].
is indicates that disturbances of synaptic homeostasis are likely associated with ASD pathogenesis. PTPRT is a candidate protein for modulating proteins that play an important role in synaptic transmission and synapse formation. Rajamani et al. generated a knocking mouse line model of the PTPRT gene. ey observed only a slight change in locomotor activities and anxiety-related behaviors in the homozygous knocking mice with PTPRT mutation, and higher social approach scores in male homozygous mice. It seems that PTPRT phosphatase function a ects mouse social behaviors which are similar to ASDs patients' symptoms [10]. Moreover, Schuurs-Hoeijmakers et al. identi ed potentially pathogenic mutations in ve genes, among them in PTPRT, in siblings with intellectual disability [11]. Further, Licis et al. found 7 contiguous single nucleotide polymorphisms at chromosome 20q12q13.12 in all the a ected individuals [9] from a single large family with manifestations of sleepwalking [12]. Our patient was diagnosed with attention de cit disorder and has stereotype movements, nervous tics, social and emotional disturbances. e above reports on gene, animal and clinical phenotype studies support our hypothesis that the PTPRT is a candidate gene for neurodevelopmental disorders, such as ADHD and ASDs. e second gene deleted in our patient is SFRS6. e protein encoded by this gene belongs to the splicing factor SR family and has been shown to bind with and modulate another member of the family − SFRS12. SFRS6 has been found mainly in the brain. ere are only several publications about the SRSF6 gene -it is proposed as a candidate gene for colorectal tumors [13] and is associated with an increased risk of nonobstructive azoospermia [14].
e L3MBTL gene is also mainly expressed in the brain. is gene encodes a member of the polycomb proteins' family which causes chromatin condensation and repression of transcription [15]. is protein is associated with cancer of hematopoietic cells [16].

CONCLUSION
In summary, the established function of the PTPRT gene suggests that haploinsu ciency of this gene may result in the clinical features observed in our patient: stereotype movements, nervous tics, social and emotional disturbances and attention-span de cits. Little is known about the SFRS12 and L3MBTL genes, but in view of the fact that these genes are expressed mainly in the brain, we suspect that their deletion may also contribute to the pathogenesis of the developmental disturbances in our patient.